Add Metal support

[antaalt]

Issue:

Here is a roadmap for getting Metal support into shader sense. Currently, I do not have a Mac available to test any of it, so it will be difficult to implement for me, but if anyone is willing to take a look, feel free to do so:

• Implement a validator which execute a metal compiler with rust binding (I believe objc2-metal is the way to go) and parse its output.
• Implement symbol processing using tree-sitter:
  • Need an available tree-sitter-metal crate on crates.io (ideally based on cpp or hlsl for sharing code with current HLSL and GLSL queries)
  • Implement queries for different types.
• Add syntax highlighting for Metal with tmlanguages in shader-validator
• BONUS: Hide each language behind a cargo feature.